3 tablespoons olive oil
1 pound mushrooms - sliced thinly
1/2 medium onion or large shallot bulb - sliced thinly
1-2 garlic cloves - minced
needles from 1 sprig fresh rosemary - chopped finely OR 1 teaspoon dried
1/2 teaspoon sea salt
Freshly ground black pepper
2 cups cheese - mozzarella (shredded) or fontina (Sliced thinly)
1/2 cup grated Parmigiano-Reggiano